Isolated avulsion fracture of the tibial attachment of the posterior cruciate ligament has been thought very rare. We also had experienced only nine cases of above injury in our center during 5.5 years from January, 1976 to June, 1981. Eight cases of them were followed for an average of the thirteen months, but one of them was eliminated from the study because follow-up study was impossible for the case. The purposes of this paper are to present eight cases of isolated avulsion fracture of the tibial attachment of the posterior cruciate ligament and to discuss the causes and mechanisms of the injury and the method of screw fixation for the avulsed fracture fragment. Seven were injured by traffic accident and one by fall on the knee. All cases seemed to be injured by the force directed against the flexed knee which violently stroke the anterior surface of the proximal end of the tibia or inferior portion of the knee and drove it backwards. We found the tear of posterior capsule only in one patient who was seeming injured by extensive force. All cases were treated operatively by means of screw fixation, and excellent results were obtained in five cases, good in two, and fair in one case.